1. Field of the Invention
The present invention relates to valves typically used on downhole tools in oil and gas wells and in particular, though not exclusively, to a water injection valve.
2. Description of Related Art
In secondary recovery of oil and gas wells it is possible to use the technique of water flooding for enhanced oil recovery. This technique relies on injecting water into the reservoir and is normally undertaken using one or more water injection wells. Such valves are typically made up to a wireline lock or retrievable packer and run to depth. A suitable valve design comprises a body including a seat against which a poppet or other closing surface of the valve can rest. The poppet is biased towards the seat(s) to hold the valve in a closed position. Water passed down the tubing string of a well bore will arrive at the poppet, and the water pressure will work against the loading of the spring and force the poppet away from the seat. The water is then directed through ports in the poppet, whereupon it takes a convoluted path to return to a central path through the valve and exit at its base.
Such valves have a number of disadvantages. Typically these valves have a spring which applies a load to the poppet to keep the valve closed. Thus when water flows an initial pressure will open the valve but there is a tendency for the valve to close again as the pressure drops when the fluid is flowing through the valve.
A further disadvantage of these valves is in the arrangement of the ports through which the water flows when the valve is open. By the nature of the design, these ports are typically small in diameter and as such they increase the pressure drop through the valve. The convoluted narrow path also causes erosional problems through the valve and increases the potential debris build up in the valve which can cause the valve to fail.
Some water injection valves are designed as high lift valves. Such valves are designed so that the poppet moves easily to the full open position with the minimum water injection flow rate. Unfortunately such a high lift design results in a low load spring design producing low resultant closing forces on the poppet mechanism. This can lead to problems with debris ingress between the poppet and seat preventing a seal.